With conventional combine harvesters, the crops that are severed by the header are conveyed to a threshing and separating assembly where a rotor is rotated within a generally cylindrical chamber to thresh the crops. Grain, seed, or the like, is loosened and separated from the other crop material and falls onto a grain pan of a cleaning assembly, which typically includes a pre-cleaning sieve disposed above a second grain pan. The grain is then conveyed to a pair of stacked sieves disposed one above the other. The grain pans and sieves are generally oscillated in a back-and-forth motion for transporting and spreading the grain across the sieves, which separate or sift the grain from tailings and “material other than grain” (MOG). The cleaned grain passes by gravity through the apertures in the sieves to underlying clean grain collecting troughs where the grain is directed to a clean grain auger.
During vibration of the sieves, a cleaning fan is typically used to blow air upwardly and rearwardly through the sieves to carry lighter elements of the MOG, or chaff, away. The heavier elements and tailings that are too large to fall through the sieves and too heavy to be blown away are moved by the vibrations of the sieves generally rearwardly along the top surface of the sieves, and towards and over the edges of the sieves to fall onto a tailings pan, which is typically a plurality of tailings collecting troughs that convey the tailings to a tailings auger trough. This trough delivers the tailings to a return conveyor that carries the tailings back to the cleaning and separating system for reprocessing.
Often times, the air from the cleaning fan is inadequate to break up clusters of grain and MOG that accumulate and roll on the sieves. This material will eventually accumulate and overload the cleaning system, whereby the sieves lose their ability to separate the MOG from the grain. This situation often requires a shutdown and manual cleaning of the system.
An improved separating and cleaning system that decreases overloading of top and bottom sieves would be a welcome advancement in the industry.